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Today’s Homework: GCF Worksheet. WARM-UP. Explain the divisibility rule for each number: 2: 3: 5: 6: 9: 10: Test the number 1,086 for divisibility with each number listed above. Today’s Homework: GCF Worksheet. WARM-UP. Explain the divisibility rule for each number:
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Today’s Homework: GCF Worksheet WARM-UP Explain the divisibility rule for each number: 2: 3: 5: 6: 9: 10: Test the number 1,086 for divisibility with each number listed above.
Today’s Homework: GCF Worksheet WARM-UP Explain the divisibility rule for each number: 2: the ones digit is even (divisible by 2) 3: the sum of the digits is divisible by 3 5: the ones digit is 5 or 10 6: the number is divisible by both 2 and 3 9: the sum of the digits is divisible by 9 10: the ones digit is 0 Test the number 1,086 for divisibility with each number listed above. 2, 3, 6
GREATEST COMMON FACTOR • What is a factor? • A factor is what a number is made of (the parts). • The numbers you multiply to get another number are factors. • Example: 2 and 6 are factors of 12. • What are other factors of 12? • 1, 3, 4, and 12 • The GCF is the LARGEST factor two numbers have in common.
HOW TO FIND GCF There are two ways of finding factors and greatest common factors: • You can list the factors of each and then find which numbers are the same in each list. • You can make a factor tree and find which factors are common in each in order to multiply them.
USING LISTS TO FIND GCF Find the GCF of 12 and 18. Use your divisibility rules to find the factors. 12: 18: 1, 2, 3, 4, 6, 12 1, 2, 3, 6, 9, 18 What is the largest common factor? 6
USING LISTS TO FIND GCF Find the GCF of 24 and 32. Use your divisibility rules to find the factors. 24: 32: 1, 2, 3, 4, 6, 8, 12, 24 1, 2, 4, 8, 16, 32 What is the largest common factor? 8
USING FACTOR TREES Find the GCF of 12 and 18. 18 12 2 6 2 9 2 3 3 3 Circle the prime factors. Which circled numbers appear in both lists? 2 and 3 (multiply them) . . . Again, GCF=6
USING FACTOR TREES Find the GCF of 24 and 32. 32 24 2 12 2 16 2 6 8 2 2 4 2 3 2 2 2 x 2 x 2 = 8 (GCF)
PRACTICE Use both methods (list and factor tree) to find the GCF of 36 and 54. GCF = 18
PROBLEM SOLVING Kaja has 32 fir, 48 cedar, and 80 maple tree seedlings to sell at the annual Agriculture Fair. He wants to display them in rows with the same number of seedlings in each row with no mixing of rows. • What is the greatest number of seedlings that he could put in each row? • How many rows of each tree seedlings will there be? GCF = 16 Fir: 2, cedar: 3, maple: 5
MATH LAB • Find the GCF of 24 and 48 by making a list. • Find the GCF of 32 and 48 by using prime factorization. • There are 84 turkey sandwiches and 63 ham sandwiches to be placed on trays. Each tray should have only one kind of sandwich, and all trays should have the same number of sandwiches. • What is the greatest number of sandwiches that can be placed on one tray? • How many trays of each type of sandwich will there be?